| Abstract |
Small cell lung cancer (SCLC) is the most aggressive form of lung cancer with poor prognosis. Combination chemotherapy remains the cornerstone in the treatment of both limited and extensive disease. Radiation therapy has been established as an adjunct to chemotherapy for limited stage disease, while in extensive disease is mainly used for the treatment of brain metastases. SCLC is trajectory with an initial good clinical response followed by rapid relapse of chemoresistant tumour and death
Since the SCLC is easily resistant to chemotherapy, second-line chemotherapy regimens are used when there is disease progression, with topotecan being the most important agent. Twenty-five years ago, we started to believe that SCLC could be included in what we call curable tumours; we had a unique staging system and effective drugs and radiation of the chest for a highly chemo - and radiation - sensitive disease . But we are 25 years later and patients seem to have the same poor prognosis. Perhaps the solution to the enigmas of this disease can be found through a better understanding of SCLC biology. Because surgical resection is not part of standard care, SCLC research using primary tumour tissue is limited to small diagnostic samples and, thus, the therapeutic benefits from the molecular analysis of these tumours are limited during the last 30 years. Drugs that are widely used in the treatment of SCLC, such as cisplatin and carboplatin, cause damage to the DNA that if the cell is unable to repair inevitably is lead to death . The ability of cells to repair the DNA damage depends on complex mechanisms that interact with the mechanisms regulating the cell cycle as well as those that control programmed cell death. ERCC1 is an enzyme which plays a key role in the GG-Nucleotide Excision Repair (GG-NER) pathway which repairs DNA adducts and other DNA helix-distorting lesions including those associated with cisplatin administration. The majority of studies on
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ERCC1 and cisplatin, in Non Small Cell Lung Cancer as well as in other solid tumours, share in common the finding that low-ERCC1 expression is associated with a better response to platinum-based chemotherapy. On the other hand, the results of in vitro studies have suggested the superiority of TC-NER pathway, in which BRCA1 protein is involved, to GG-NER pathway in predicting platinum resistance. Modulation of BRCA1 expression leads to modification of TC-NER and, hence, to radio- and chemo-resistance. BRCA1 is also involved in homologous recombination repair and non-homologous end joining, in response to DNA damage and may be a regulator of mitotic spindle assembly, as BRCA1 and b-tubulin co-localize to the microtubules of the mitotic spindle and to the centrosomes. In addition, recent data have shown that import and export transporters involved in maintenance of copper
homeostasis are also involved in the transport of cisplatin. Especially, overexpression of the P-type transporter ATP7B conferred cisplatin resistance associated with decreased intracellular accumulation of cisplatin and carboplatin. Also, the role of PKM2 in resistance to platinum analogs is recently under extensive investigation; PKM2 replaces the specific isoforms (type L, R, and M1) during tumourigenesis and substitution is under the control of the transcription factor C-MYC. The overexpression of MYC proteins in SCLC is largely a result of gene amplification and leads to more rapid proliferation and loss of terminal differentiation. C-MYC overexpression occurs in 16–32% of SCLC and in 40% of cell lines established from patients whose disease progressed after chemotherapy . Finally, several mechanisms of resistance have been suggested to involve DNA topoisomerase I and II, which are the target of several compounds, including topoisomerase-I inhibitors (such as irinotecan and topotecan) as well as topoisomerase-II inhibitors (such as etoposide and doxorubicin). This study retrospectively analyzes the predictive value on both
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response to treatment and survival of BRCA1, ERCC1, ATP7B, PKM2, TOPOI, TOPΟ-IIA, TOPOIIB and C-MYC mRNA levels, as they are detected by real-time PCR in SCLC patients treated with platinum-based combination chemotherapy with or without chest radiotherapy. In the group of patients with limited disease, shorter progression free survival was found for those who had high mRNA expression of ERCC, PKM2, TOPO-I, TOPO- IIA and TOPO-IIB compared to patients with low mRNA expression of the same genes . Furthermore, the median overall survival was significantly reduced in patients who had high mRNA expression of ERCC, PKM2, TOPO- IIA and TOPO-IIB compared to patients who had low expression of the same genes. For patients with extensive disease, the only statistically significant correlation was found between mRNA expression of TOPO- IIB and overall survival. Moreover, for the limited-stage SCLC, 26 patients who had high mRNA expression of the four genes ERCC1, PKM2, TOPO-IIA and TOPO-IIB had significantly shorter progression free survival compared to 25 patients with low mRNA of the same genes. The same group of patients had also significantly shorter overall survival compared to patients with low expression levels of the four genes. Similar results were found for patients with extensive-stage SCLC. Based on these findings we can characterize the high mRNA expression of ERCC1, PKM2, TOPO-IIA and TOPO-IIB as unfavorable gene signature and the low mRNA expression as a favorable gene signature for progression free survival and overall survival of patients with SCLC regardless of the stage of the disease. In the multivariate analysis, the unfavorable gene signature was an independent predictor of shorter progression free survival and overall survival for both stages of the disease. Through this study we have demonstrated that with the use of pharmacognomics analysis we can identify subgroups of patients with SCLC,
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which are more or less likely to benefit from chemotherapy with platinum-etoposide combinational therapy.
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